petrol or diesel

Gnome

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I've driven both, Petrol wins every time in my book.

Sure Diesel has got torque but it smokes, it stinks, it's noisy, the engine is incredibly heavy so it's slow to pick up revs and it lacks in the power department, it's just the nature of diesel.

Petrol cars have only 1 disadvantage, low torque (when compared with a diesel), makes the diesel look like a fat old cow, it's strong but slow.
 

Shake&Bake

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Stinks? Noisy? Slow to pick up revs and lacks in the power department? Not even close in my experience :)
 

HapticSimian

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That's the skewed impression you get when you compare your <insert small, rev-happy petrol chariot here> with Oom Frikkie's faithful bakkie on the farm.

I challenge you to take a current 330d for a spin & come back with the same opinion.
 

BTTB

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@Gnome.
That was also my impression for many years. Like the old Isuzu Bakkie which you could hear clattering along from about a mile away.:D

However things have changed somewhat with Diesel vehicles.
We now have common rail diesel technology with motors that are quiet with even more torque than what they had before. Low sulphur diesel that does not smoke at all.
I can add to that list, but I think you should do some investigation into the latest diesel vehicles on the market.
Diesel is a bit cheaper than petrol and the fuel economy on a diesel motor in some models is far lighter than petrol.
 

Gnome

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Stinks? Noisy? Slow to pick up revs and lacks in the power department? Not even close in my experience :)

You've probably only driven crappy petrol cars, diesel engines are by their nature heavy (because the engine deals with high compressions ratio's) and low in power (because the engine is heavy it's restricted to low RPM), low rpm = low power because power is a product of rpm and torque, it's like a mule compared to a race horse. One is strong but slow the other is weak but fast. Why do you think Honda engines make so much power, it's because they rev to 9000rpm, while you've shifted twice in your diesel power engine, the 9000rpm rever is still climbing up the ladder making more power by the second.

That's the skewed impression you get when you compare your <insert small, rev-happy petrol chariot here> with Oom Frikkie's faithful bakkie on the farm.

I challenge you to take a current 330d for a spin & come back with the same opinion.

The problem is you need to compare petrol cars in the same price region to the 330d obviously it's not a bad car, there are just better options in that price range. Take a Honda Civic Type R or some other petrol powered car that makes a lot of power for a drive and you'll see the appeal. I used the Honda as an example because I like N/A and I like high-rpm engines, there's nothing like putting the car into 2nd and it keeps going, and going and going, then into 3rd, same story, it's really something to experience.

Torque is what you feel, that feeling that pushes you back into your seat, the only problem is a car can do that and still not move very quickly which is pretty much what a diesel car does, don't take me wrong you get some quick diesel cars but in the same price range you can easily find a petrol car and it's making more power, getting to 0-100 faster and it's got a higher top end speed.

You don't buy a diesel because you want performance, if you do then you need to really get out and test drive the proper petrol models, read some online review before you go out for a performance model.

@Gnome.
That was also my impression for many years. Like the old Isuzu Bakkie which you could hear clattering along from about a mile away.:D

However things have changed somewhat with Diesel vehicles.
We now have common rail diesel technology with motors that are quiet with even more torque than what they had before. Low sulphur diesel that does not smoke at all.
I can add to that list, but I think you should do some investigation into the latest diesel vehicles on the market.
Diesel is a bit cheaper than petrol and the fuel economy on a diesel motor in some models is far lighter than petrol.

Meh, they still smoke, if I take the latest and greatest golfs I see on the road, if a petrol car smoked like that, I'd think about overhaul immediately still I'm a young person so I like cars with a little bit of excitement.

If you like a slow family type car then it's all good, now I don't mean slow as in it's terrible but I look at the price then look at the performance, then I look at the petrol cars in the same region and I'm wondering why I would take the diesel, it's more expensive and it's making 1/2 the power. And it's not like they are more reliable, the only thing that's "great" about them is the fuel saving and torque imho.
 
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alkit

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I hope I don't get flamed for this, but could someone please explain to me what the benefit of torque is?
I was told that the more KW a car has, the faster it can accelerate, and torque is oinly to keep it going.
Can anyone enlighten me as to why torque is so important?

Also, has anyone taken into consideration that not only is the fuel economy better on a diesel, but diesel fuel itself costs less per litre... so unless it is majorly more expensive to service the car, how could it possibly be cheaper to get petrol?
 

HapticSimian

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I hope I don't get flamed for this, but could someone please explain to me what the benefit of torque is?
I was told that the more KW a car has, the faster it can accelerate, and torque is oinly to keep it going.
Can anyone enlighten me as to why torque is so important?
It's a very difficult concept to explain. Torque (Nm) is essentially the amount of force something is twisted with, whilst power (kW) is an indicator of the rate at which 'work' can be done. So a low kW/high torque diesel delivers huge bursts of turning power to the driveline rather slowly, whilst a petrol is comparatively limp-wristed but punches a hell of a lot faster...

Also, has anyone taken into consideration that not only is the fuel economy better on a diesel, but diesel fuel itself costs less per litre... so unless it is majorly more expensive to service the car, how could it possibly be cheaper to get petrol?
I don't know what the current situation is, but diesel was significantly more pricey than petrol not so long ago. The biggest factor is that you pay more initially to buy a diesel than you do a comparative petrol.

EDIT

No flaming necessary - there are no stupid questions, only stupid people. ;)
 
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Gnome

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So a low kW/high torque diesel delivers huge bursts of turning power to the driveline rather slowly, whilst a petrol is comparatively limp-wristed but punches a hell of a lot faster...

Good, simple explanation!

I'll just add, if you take a water wheel, it could generate more than 1000 NM of torque and you could essentially lift up a house with that but at the same time that waterwheel is generating virtually no power like 10hp or whatever because it is moving at 1rpm, sure you could pull around just about any mass but you'll be doing it at a really, really slow speed :p
 

Sensorei

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Kilowatts is how fast you hit the Wall. Torque is how far you take the wall when you hit it.
 

alkit

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It's a very difficult concept to explain. Torque (Nm) is essentially the amount of force something is twisted with, whilst power (kW) is an indicator of the rate at which 'work' can be done. So a low kW/high torque diesel delivers huge bursts of turning power to the driveline rather slowly, whilst a petrol is comparatively limp-wristed but punches a hell of a lot faster...


I don't know what the current situation is, but diesel was significantly more pricey than petrol not so long ago. The biggest factor is that you pay more initially to buy a diesel than you do a comparative petrol.

EDIT

No flaming necessary - there are no stupid questions, only stupid people. ;)

Thanks for the explanation, but what does that mean in actual driving experience?
Does more torque mean more acceleration, or more speed? Or something else?

Thanks
 

HapticSimian

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Thanks for the explanation, but what does that mean in actual driving experience?
Does more torque mean more acceleration, or more speed? Or something else?

Thanks

Try to get a drive in a modern turbo-diesel - it's just a different 'type' of drive. Again, it's difficult to put the sensation into words... Modern diesels tend to have very strong in-gear acceleration (330d is quicker than an M3 in certain ranges up here on the Highveld) but from standstill and on extended runs their short rev-range works against them. Remember that a diesel will only rev to 4,500 or maybe 5,000 rpm where even a 'normal' petrol engine would go to 7,000+ rpm.

Diesels just tend to feel 'effortless', similar to how take-off feels in a Boeing. You get a sense of power that petrol can't easily match.
 

Sensorei

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Reading posts here will not give you an understanding of a turbo diesel. There's some great info here but you have to drive one to understand. Go for a test drive!
 

HapticSimian

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:D

I think the current appeal of diesel is due in a large part to the incredible progress the manufacturers have made. Think about it - petrol internal combustion is a very mature technology. BMW were churning out 1,000kW in qualifying trim with 1.5l 4 cylinder turbos in '82/'83 F1 cars.

But diesel has come, in the space of less than 10 years, from being noisy, smelly, smoking, rattling tractors to winning Le Mans.
 

BCO

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:D

I think the current appeal of diesel is due in a large part to the incredible progress the manufacturers have made. Think about it - petrol internal combustion is a very mature technology. BMW were churning out 1,000kW in qualifying trim with 1.5l 4 cylinder turbos in '82/'83 F1 cars.

But diesel has come, in the space of less than 10 years, from being noisy, smelly, smoking, rattling tractors to winning Le Mans.

They're still noisy, smelly, smoking, rattling tractors that are winning Le Mans. :p
 

HapticSimian

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... that can give you mild whiplash if you don't respect 'teh throttle pedal'... sooooooo addictive. :)
 

Paul_S

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One cannot compare a turbo charged diesel to a normally aspirated petrol engine.
Take the turbo off the diesel and then you can compare it directly to a petrol engine.

Or if you want to compare a turbo diesel to a petrol equivalent then pick something like the Golf GTI that has a turbo charged petrol engine.

Without a turbo changer the diesel powered cars we now use would be terrible to drive. Very low power and mediocre torque.

Forced induction != normally aspirated :rolleyes:
 

HapticSimian

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One cannot compare a turbo charged diesel to a normally aspirated petrol engine.

Oh, but one can. You're already comparing two types of engines that are inherently different. Adding forced induction is exactly what enables one to compare petrol and diesel, at least as far as performance and market appeal goes. ;)
 

UtterNutter

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I agree with Paul_S to an extent in that on one side of the coin you can't really compare a turbo diesel to a NA petrol.

HOWEVER: due to the differences in the technicalities of the engines (not just the fuel) and of the combustion process, diesel engines can be turbocharged so much more easily (and to a greater degree) than petrol engines (diesels don't have throttle butterflies, no restricting of boost pressure, stronger-built components etc), thus tubocharging is an inherent part of the diesel engine (and has been for a long time).
 
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UtterNutter

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I drive a 330d. Its engine is NOT a performance engine. However, having 500 Nm in that car transforms the car into a performance car, even if its engine isn't.

One needs to drive a MODERN diesel to fully understand the difference. The engine is of such a different character (compared to a petrol engine) and it's difficult to explain power and torque in a non-scientific manner.
 
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